The present invention addresses a problem encountered by just about every person at one time or another—drawing a bath and discovering there is insufficient hot water available to fill the bathtub at a desired level and at a desired temperature only after the bathtub is fully or partially filled. There are myriad reasons for why there is insufficient hot water available, such as recent hot water consumption by various appliances and/or people. For example, unbeknownst to the bather, another person or appliance has been using hot water (or at least more hot water than the bather thought was being used), depleting the hot water in the water heater tank.
Typically, a bather will turn on the hot water supply valve or turn a single water control valve to the hot water position and start running water into the bathtub with the drain open until hot water begins to be supplied at the faucet. The bather then adjusts the water supply (either via adding cold water via a second cold water control valve or adjusting the position of a single control value) to obtain the desired temperature and closes the drain to fill the bathtub. The bather then typically walks away while the bathtub fills with water, expecting to return a short time later with a bathtub of hot or warm water. In the meanwhile, the hot water supply becomes depleted, causing the hot water supplied to the bathtub to become cooler and cooler. When the bather returns, she finds the bathtub full of lukewarm water. This is typically followed by some unpleasant verbalization and opening of the drain to drain out the lukewarm water.
There are known solutions to the lukewarm bath, but most are not viable. In the context of a single-family household setting, one solution is to become single again, thereby eliminating other hot water consumers. However, this option generally doesn't sit well with spouses and children. Another solution is to yell at any teenagers in the house, who believe a long shower makes up for a short attention span (as pertains to parents). A potentially more realistic solution is to buy a larger hot water tank, or better yet, multiple hot water tanks. As with the other solutions, this usually is not viable, due to space restrictions and other reasons, such as lack of money due to the spending habits of the spouse and/or teenagers and fear of large payments to the local energy utility. Another option is to buy a tankless water heater, but this may be cost prohibited for many families, particularly those with teenagers who prefer texting to talking. Finally, another option is to boil some water and add it to the bath, but since the bather is already boiling mad she often doesn't have the patience or energy to do so.